1. Field of the Invention
The present invention relates to an optical fiber based communications network, and more particularly to an optical switch arrangement that provides reduced optical losses and reliable switching.
2. Discussion of the Related Art
In recent years, Internet usage and other computer communications modes have become widespread. Moreover, audio and video applications that are becoming increasingly popular require large amounts of information (bandwidth) to be transferred. As a result, demands on the bandwidth supported by communications systems have skyrocketed. Optical communication systems have become increasingly important to fulfill such needs.
Such optical communications systems are capable of rapidly transferring large volumes of information by converting electrical signals into light signals and transmitting the light through optical fibers. The optical fibers form a network of optical paths between different geographic locations (e.g., different metropolitan areas). To route the information between the different locations, the information is switched between different optical paths. Conventionally, the information is switched by converting the optical signals into electrical signals, switching the electrical signals, reconverting the electrical signals to optical signals and re-transmitting the optical signals onto the desired optical path.
With advances in optical communications technology, optical switches (such as micro-mirror switches) are being developed to provide large switching fabrics that operate in the optical domain and can switch more information faster than electrical switches. A common problem of micro-mirror switches, as well as other optical switches, is achieving efficient coupling between the inputted and outputted optical signals with the switch fabric.
Input and output coupling may be achieved by aligning an optical fiber and a collimating lens at both the inputs and the outputs to be focused on an array or arrays of mirrors. For example, large port count cross-connect micro-mirror switches might have a considerable optical path between a given input and output (more than 10 cm but in most cases less than 50 cm). In order to reduce losses between inputs and outputs, the optical path between inputs and outputs should be reduced to maintain sufficiently narrow beam widths for the optical widths of all the optical elements. However, as the distance between inputs and outputs decreases, the range of angles over which the micro-mirrors have to move in order to switch inputs to outputs increases. Micro-mirrors typically should not be repeatedly tilted to or near an angle that causes damage to the micro-mirrors or switching reliability may suffer.
Moreover, applications involving long distance optical paths at high bit rates ( greater than Gbs) require the use of optical fibers requiring having tight fabrication tolerances to avoid optical loss if strict angular tolerances (within 0.01 degrees) are not achieved. In addition, such optical fibers have a small core diameter and a small numerical aperture. The small numerical aperture implies that the cone of light that can be accepted by the optical fiber is narrow. Hence, for reasons such as these, through-put is easily decreased if the light is not properly focused or if the light is diminished in intensity, thereby potentially causing signal loss or signal deterioration.
To successfully operate optical switches using mirrors, the mirrors must be precisely aligned and the distance between mirrors reflecting a beam to connect optical links should be minimized. If the angular position of the mirrors are off and/or if the mirrors are too far apart, some or all of the light from the input will not reach the selected output. There remains a need in the art for an optical switch having a compact and reliable arrangement of steerable mirrors.
Accordingly, the present invention is directed to an optical switch that substantially obviates one or more of the problems due to limitations and disadvantages of the related art.
An objective of the present invention is to provide precise optical switching having reliable angular responsiveness by minimizing a mirror""s range of movement near a critical tilt angle of the mirror.
Another objective of the present invention is to maintain precision optical switching by preventing a mirror from tilting to an angle that is near the mirror""s critical tilt angle.
Another objective of the present invention is to reduce optical losses by shortening the distance between the inputs and the outputs of an optical switch.
Another objective of the present invention is to provide both reliable and precise control in optical switching using mirrors.
Additional features and advantages of the invention will be set forth in the description which follows, and in part will be apparent from the description, or may be learned by practice of the invention. The objectives and other advantages of the invention will be realized and attained by the structure particularly pointed out in the written description and claims hereof as well as the appended drawings.
To achieve these and other advantages and in accordance with the purpose of the present invention, as embodied and broadly described, an optically switched network element comprises a plurality of optical inputs; a plurality of optical outputs; an optical switching mechanism for selectively coupling input optical signals from the plurality of optical inputs to said plurality of optical outputs, said optical switching mechanism including an array of at least two steerable mirrors, wherein at least one of the steerable mirrors has an offset angle.
In another aspect, a method of switching optical signals by inputting the received optical signals into an optical switch; switching the received optical signals within the optical switch using at least two mirror arrays; and outputting the received optical signals from the optical switch to output optical fibers, wherein at least one of the mirrors in the arrays having an offset angle greater than zero prior to inputting the received optical signals.
Another aspect is an optical switch having a plurality of inputs emitting input beams within an optical switch; a plurality of outputs receiving output beams emitted from the optical switch; and an optical switching mechanism for selectively coupling input beams from the plurality of inputs to the plurality of outputs as output beams, the optical switching mechanism comprising at least two arrays of steerable mirrors, wherein at least one of the steerable mirrors has an offset angle greater than zero degrees.
Another aspect is an optical switch having a plurality of optical inputs; a plurality of optical outputs; an optical switching mechanism for selectively coupling input optical signals from the plurality of optical inputs to the plurality of optical outputs, the optical switching mechanism including an array of at least two steerable mirrors on a substrate; and control electrodes on the substrate for steering the mirrors, and static DC potentials are applied to the control electrodes of a mirror and subsequent control signals for steering the mirror are superimposed on the static DC potential.
It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory and are intended to provide further explanation of the invention as claimed.